The Excited State Properties of Thermally Activated Delayed Fluorescence Emitters: A Computational Study Towards Molecular Design

热激活延迟荧光发射体的激发态特性：分子设计的计算研究

• 批准号: EP/N028511/1
• 负责人: Thomas Penfold
• 金额: $ 10.97万
• 依托单位: Newcastle University
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2016
• 资助国家: 英国
• 起止时间: 2016 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FN028511%2F1
• 关键词: Excited; State; Properties; Thermally; Activated

Lighting and displays form essential parts of our daily lives and consume approximately 20% of the electricity used worldwide. Consequently, significant energy and cost savings can be achieved by improving the efficiency of these devices. Due to their lightweight, flexibility and high-performance optical and electrical properties, Organic Light-Emitting Diodes (OLEDs) are a central focus of this research and have huge potential for application in technologies such as smart phones, televisions and lighting. OLEDs are, like classic LEDs, able to transform electrical energy into visible, ultra-violet (UV) or near Infra-red (NIR) light. However, unlike LEDs, OLEDs consist of several very thin, stacked layers organic materials and do not rely on small, point-shaped single crystals. In addition, organic systems are highly attractive for mass production stemming from their ability to be deposited on a variety of low-cost substrates such as glass, plastic or metal foils, and due to their relative ease of processing. Indeed, because production costs of these devices are typically dominated by fabrication and packaging, the relatively weak van der Waals bonded organic films also create the opportunity for a new suite of innovative fabrication methods, including direct printing through the use of contact with stamps, or alternatively via ink-jets and other solution-based methods. Even though OLEDs have huge potential to achieve a higher energy efficiency than LEDs and may also be processed under more sustainable conditions, today's state of the art white OLEDs still have higher power consumption than white LEDs. In terms of efficiency, initial attempts to implement OLEDs based upon purely organic materials were restricted by the type of excited state which emits the light. Indeed, upon electrical excitation 25% of the emitting molecules are in a so called singlet excited state, while 75% are in triplet excited states. However, conventional organic materials cannot emit from the triplet excited states, meaning that only a maximum efficiency of 25% could be achieved. An extensive research effort successfully led to 2nd generation (so called phosphorescence) OLEDs that use heavy metals to promote light emission from the triplet states and, in principal, achieve 100% efficiency. However, until now the only phosphorescent materials found practically useful are iridium and platinum complexes that are unappealing for commercial applications due to their high cost and low abundance.This research proposal seeks to investigate, using multi-scale modelling, the fundamental properties crucial to molecules and materials for a new class of OLEDs that exploits thermally activated delayed fluorescence. This exploits a small energy gap between the two emitting states (singlet and triplet) so that thermal energy can transfer population from the triplet state to the singlet state. Importantly this mechanism opens the possibility to achieve, in principal, 100% efficiency and crucially precipitates the potential to return to materials containing only lighter more abundant elements, such as organic molecules. By combing quantum chemistry, molecular and quantum dynamics, this multidisciplinary approach will produce a detailed physical and chemical understanding of the material properties on a wide variety of time and length scales. Critically, these simulations will underpin our understanding of the properties that lead to their efficiency. This bottom up approach will consequently provide important insight into achieving systematic material design with the potential for vastly improved and cheaper devices.

照明和显示器构成了我们日常生活的重要组成部分，消耗了全球约20%的电力。因此，通过提高这些设备的效率，可以实现显著的能源和成本节约。有机发光二极管(OLED)由于其轻巧、灵活和高性能的光学和电学特性，是本研究的重点，在智能手机、电视和照明等技术中具有巨大的应用潜力。与传统LED一样，OLED能够将电能转换为可见光、紫外线(UV)或近红外(NIR)光。然而，与LED不同的是，OLED由几个非常薄的、堆叠的有机材料层组成，不依赖于小的点状单晶。此外，有机体系对大规模生产非常有吸引力，因为它们能够沉积在各种低成本的衬底上，如玻璃、塑料或金属箔，并且由于它们相对容易加工。事实上，由于这些设备的生产成本通常由制造和封装主导，相对较弱的范德华粘合有机薄膜也为一系列新的创新制造方法创造了机会，包括通过使用与邮票接触的方式直接打印，或者通过喷墨和其他基于溶液的方法。尽管OLED具有实现比LED更高的能效的巨大潜力，而且还可以在更可持续的条件下加工，但当今最先进的白色OLED仍然比白色LED具有更高的功耗。在效率方面，基于纯有机材料实现OLED的最初尝试受到发射光的激发态类型的限制。事实上，在电激发下，25%的发射分子处于所谓的单重态激发态，而75%的发射分子处于三重态激发态。然而，传统的有机材料不能从三重态激发态发射，这意味着只能达到25%的最大效率。一项广泛的研究工作成功地导致了第二代(所谓的磷光)OLED，它使用重金属来促进三重态的光发射，原则上实现了100%的效率。然而，到目前为止，发现的唯一实用的磷光材料是由于高成本和低丰度而对商业应用不具吸引力的铱和铂配合物。本研究计划试图通过多尺度模拟来研究对利用热激活延迟荧光的新型OLED的分子和材料至关重要的基本性质。这利用了两个发射态(单重态和三重态)之间的小能量间隙，使得热能可以将布居从三重态转移到单重态。重要的是，这一机制打开了原则上实现100%效率的可能性，并关键地使人们有可能返回到只包含更轻、更丰富元素的材料，如有机分子。通过结合量子化学、分子和量子动力学，这种多学科的方法将在各种时间和长度尺度上产生对材料性质的详细物理和化学理解。至关重要的是，这些模拟将巩固我们对导致其效率的特性的理解。因此，这种自下而上的方法将为实现系统的材料设计提供重要的见解，并有可能极大地改进和降低设备成本。

项目成果

World Scientific Reference on Spin in Organics - Volume 3: Magnetic Field Effects

有机物自旋世界科学参考书 - 第 3 卷：磁场效应

• DOI: 10.1142/9789813230194_0006
• 发表时间: 2018
• 作者: Dias F

Rapid predictions of the colour purity of luminescent organic molecules

• DOI: 10.1039/d1tc04748e
• 发表时间: 2022-01-07
• 期刊: JOURNAL OF MATERIALS CHEMISTRY C
• 影响因子: 6.4
• 作者: Ahmad, Shawana A.;Eng, Julien;Penfold, Thomas J.
• 通讯作者: Penfold, Thomas J.